At least seven people died and several others were injured after a massive explosion occurred inside a house in Bihar’s Bhagalpur district on Thursday night, ANI reported.

The explosion took place at a house in Kajwali Chak village under Tatarpur police station of Bhagalpur, according to News18. The blast was so powerful that four houses collapsed in the locality.

The authorities have not been able to confirm the cause of the explosion yet.

Bhagalpur District Magistrate Subrat Kumar Sen told reporters that on prima facie investigation it seemed like people in the house were involved in making firecrackers. However, Bhagalpur range Deputy Inspector General of Police Sujit Kumar said that the explosion might have occurred during manufacture of country-made crude bombs.

“As the nature of the blast was so intense, we believe that the quantity of the explosives was very high,” Kumar said, according to News18. He added that the police were recording statements of the locals and a forensics team had gathered evidence from the site of the blast.

Of the seven victims, two were identified as Ganesh Prasad Singh (60) and Urmila Devi (65), while the identities of the five others have not been ascertained yet.

In a tweet, Prime Minister Narendra Modi expressed grief and said that he has spoken to Bihar Chief Minister Nitish Kumar about the tragic incident.

“The administration is carrying out relief operations and the victims are being given all possible assistance,” Modi wrote.